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                [Usaco2007 Mar]Cow Traffic 奶牛交通                </h1>
                <p>时间限制：5s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：64MB</p>			</div>
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                                <h3>题目描述</h3><p><p><span style="font-size: medium">农场中,由于奶牛数量的迅速增长,通往奶牛宿舍的道路也出现了严重的交通拥堵问题.FJ打算找出最忙碌的道路来重点整治. 这个牧区包括一个由M (1 &le; M &le; 50,000)条单行道路(有向)组成的网络,以及 N (1 &le; N &le; 5,000)个交叉路口(编号为1..N),每一条道路连接两个不同的交叉路口.奶牛宿舍位于第N个路口.每一条道路都由编号较小的路口通向编号较大的路口.这样就可以避免网络中出现环.显而易见,所有道路都通向奶牛宿舍.而两个交叉路口可能由不止一条边连接. 在准备睡觉的时候,所有奶牛都从他们各自所在的交叉路口走向奶牛宿舍,奶牛只会在入度为0的路口,且所有入度为0的路口都会有奶牛. 帮助FJ找出最忙碌的道路,即计算所有路径中通过某条道路的最大次数.答案保证可以用32位整数存储. </span></p></p><hr/><h3>输入格式</h3><p><p><span style="font-size: medium">第一行:两个用空格隔开的整数:N,M. </span></p>
<p><span style="font-size: medium">第二行到第M+1行:每行两个用空格隔开的整数ai,bi,表示一条道路从ai到bi.</span></p></p><hr/><h3>输出格式</h3><p><p><span style="font-size: medium">第一行: 一个整数,表示所有路径中通过某条道路的最大次数. </span></p></p><hr/><h3>样例输入</h3><pre>7 7
1 3
3 4
3 5
4 6
2 3
5 6
6 7
</pre><hr/><h3>样例输出</h3><pre>4
样例说明: 

    1   4
     \ / \
      3   6 -- 7
     / \ /
    2   5
通向奶牛宿舍的所有路径: 

    1 3 4 6 7
    1 3 5 6 7
    2 3 4 6 7
    2 3 5 6 7
</pre><hr/><h3>提示</h3><p>没有写明提示</p><hr/><h3>题目来源</h3><p>Silver</p>
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